The present invention relates to a light-emitting device that converts electric energy into light to be useful for indicating elements, display devices, backlights, electro-photographies, illumination light sources, recording light sources, exposing light sources, reading light sources, road signs and markings, signboards, interiors, optical communications, etc. The present invention further relates to a heterocyclic compound usable for the light-emitting device, especially for an organic electroluminescence device.
Recently, various display devices have been widely studied. In particular, organic electroluminescence (EL) devices are advantageous in that they can emit light with high luminance by a lowered applying voltage, whereby much attention has been paid thereto. For example, a light-emitting device comprising organic thin layers provided by vapor-depositing organic compounds has been disclosed in Applied Physics Letters, 51, 913 (1987). This light-emitting device has a structure where an electron-transporting material of tris(8-hydroxyquinolinato) aluminum complex (Alq) and a hole-transporting material of an amine compound are disposed between electrodes as a laminate, thereby exhibiting more excellent light-emitting properties than that of conventional light-emitting devices having a single-layer structure.
The above light-emitting device having the laminate structure can be improved with respect to light-emitting efficiency by doping the device with a fluorescent compound such as a coumarin dye, etc. as disclosed in Journal of Applied Physics, Vol.65, Page 3610, 1989, etc. Emission wavelength can be controlled by changing the fluorescent compound. However, in the case of using Alq as a charge-transporting material for the light-emitting device, particularly for a blue light-emitting device, green light emission due to Alq is observed in addition to light emission by the doped fluorescent compound when the driving voltage is increased to obtain high luminance. As a result, the light-emitting device is reduced in the color purity. Therefore, it has been desired to develop a host material that can suppress the reduction of the color purity, and for example, Japanese Patent Laid-Open No. 10-92578 and U.S. Pat. No. 5,766,779 have disclosed that a particular indole derivative can be used as the host material to provide a blue light-emitting device high in the color purity. However, the device using the indole derivative needs high driving voltage to obtain a high luminance, and thus it has been desirable to develop a material, a light-emitting device using the same providing high luminance with low driving voltage.
Further, though it is known that the light-emitting efficiency of the light-emitting device can be improved by a method using a hole-blocking material such as 3-(biphenyl-4-yl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ), bathocuproine (BCP), etc., the device using the hole-blocking material is poor in durability. In particular, such light-emitting device is disadvantageous in that the properties of the device are worsened during high temperature storage or continuous operation.
Among the conventional light-emitting devices, such that comprises a charge-transporting material doped with a small amount of a fluorescent compound is excellent in the color purity and the light-emitting efficiency. However, such a light-emitting device is poor in reproducibility of the light emission. Further, the fluorescent compound is low in durability, whereby reduction of the luminance, change of the emission color, etc. is caused when the device is used for a long-term. Proposal has been made to overcome such problems is a method of using a material having both of a charge-transporting property and a light-emitting property. However, in the case of using the fluorescent compound at a high concentration, the device using the material is poor in luminance because of concentration quenching, association of the fluorescent compound, etc.
Although the organic layer of the organic light-emitting device may be formed by a vapor deposition method, a sputtering method, a coating method, etc., the organic layer is desirably formed by the coating method from the viewpoints of simplification of production processes, improvement of workability, application to a flexible device having a large emitting area, etc. However, the organic layer has been generally formed by the vapor deposition method in the conventional organic light-emitting devices high in the luminance, and the light-emitting devices produced by the coating method have been poor in the luminance and the light-emitting efficiency.
An object of the present invention is to provide a light-emitting device excellent in light-emitting properties, durability in repeated use and color purity. Another object of the present invention is to provide a heterocyclic compound that is usable for the light-emitting device and has a wide applicability for an electronic device, etc.
As a result of intense research in view of the above objects, the inventor has found that a light-emitting device using a particular compound having a purine skeleton is excellent in light-emitting properties, durability and color purity. The present invention has been accomplished by the finding.
Thus, a light-emitting device of the present invention comprises a pair of electrodes and one or more organic layers disposed between the electrodes, the one or more organic layers comprising a light-emitting layer, wherein at least one of the one or more organic layers comprises a compound having a purine skeleton represented by the following formula (I). 
In the formula (I), R11 represents a substituent; R12 represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group; R13 represents a hydrogen atom or a substituent; n represents an integer of 0 to 2; L represents a single bond or a linking group; and m represents an integer of 2 or more.
It is preferred that the compound represented by the formula (I) is further represented by any one of the following formulae (II) and (XI). 
In the formula (II), R21, R22 and R23 represent a substituent, respectively; R24, R25 and R26 represent a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group, respectively; R27, R28 and R29 represent a hydrogen atom or a substituent, respectively; n21, n22 and n23 represent an integer of 0 to 2, respectively; L1, L2 and L3 represent a single bond or a linking group, respectively; and Y represents a nitrogen atom or a 1,3,5-benzenetriyl group. 
In the formula (XI), R111 and R112 represent a substituent, respectively; R113 and R114 represent a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group, respectively; R115 and R116 represent a hydrogen atom or a substituent, respectively; n111 and n112 represent an integer of 0 to 2, respectively; Z1 and Z2 represent an arylene group or a divalent aromatic heterocyclic group, respectively; L111 represents a single bond or a linking group; and L112 and L113 represent a single bond, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94N(R117)xe2x80x94, respectively, in which R117 represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group.
It is preferred that the compound represented by the formula (II) is furthermore represented by any one of the following formulae (III) and (IV). It is preferred that the compound represented by the formula (XI) is furthermore represented by any one of the following formulae (XII) and (XIII). The heterocyclic compound of the present invention represented by the formula (III), (IV), (XII) or (XIII) has a wide applicability for an electronic device, etc. 
In the formula (III), R31, R32 and R33 represent a substituent, respectively; R34, R35 and R36 represent a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group, respectively; and n31, n32 and n33 represent an integer of 0 to 2, respectively. 
In the formula (IV), R41, R42 and R43 represent a substituent, respectively; R44, R45 and R46 represent a hydrogen atom or a substituent, respectively; and n41, n42 and n43 represent an integer of 0 to 2, respectively. 
In the formula (XII), R121 and R122 represent a substituent, respectively; R123 and R124 represent a hydrogen atom or a substituent, respectively; R125 and R126 represent a substituent, respectively; n121 and n122 represent an integer of 0 to 2, respectively; n125 and n126 represent an integer of 0 to 4, respectively; and L121 represents a single bond or a linking group. 
In the formula (XIII), R131 and R132 represent a hydrogen atom or a substituent, respectively; R133 and R134 represent a hydrogen atom or a substituent, respectively; R135 and R136 represent a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group, respectively; R137 and R138 represent a substituent, respectively; n137 and n138 represent an integer of 0 to 4, respectively; L131 represents a single bond or a linking group; and L132 and L133 represent a single bond, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94N(R139)xe2x80x94, respectively, in which R139 represents a hydrogen atom, an aliphatic hydrocarbon group, an aryl group or a heterocyclic group.
In the organic layer comprising the compound represented by the formula (I), the compound is preferably dispersed in a polymer. Further, it is preferred that the organic layer comprising the compound represented by the formula (I) further comprises a transition metal complex. The transition metal complex is preferably an ortho-metallation complex. Weight ratio of the compound represented by the formula (I) is preferably 1 to 99 weight % based on the total of the organic layer comprising the compound when the compound is used as a host material. Further, the weight ratio is preferably 1 to 100 weight % when the compound is used as a material other than the host material.
Incidentally, although the compound having the purine skeleton according to the present invention falls within claims attached to the specification of Japanese Patent Laid-Open No. 2000-63818, the compound according to the present invention is not recited concretely or specifically in the specification of Japanese Patent Laid-Open No. 2000-63818 so that a structure, superior result and advantage of the subject matter of the present invention have been unexpected by those skilled in the art based on the specification.